HTTP header common structure

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Last updated 2016-10-05
Replaced by draft-ietf-httpbis-header-structure
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Network Working Group                                           PH. Kamp
Internet-Draft                                 The Varnish Cache Project
Intended status: Informational                          October 05, 2016
Expires: April 8, 2017

                      HTTP header common structure


   An abstract data model for HTTP headers, "Common Structure", and a
   HTTP/1 serialization of it, generalized from current HTTP headers.

Status of This Memo

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   This Internet-Draft will expire on April 8, 2017.

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Kamp                      Expires April 8, 2017                 [Page 1]
Internet-Draft                     I-D                      October 2016

1.  Introduction

   The HTTP protocol does not impose any structure or datamodel on the
   information in HTTP headers, the HTTP/1 serialization is the
   datamodel: An ASCII string without control characters.

   HTTP header definitions specify how the string must be formatted and
   while families of similar headers exist, it still requires an
   uncomfortable large number of bespoke parser and validation routines
   to process HTTP traffic correctly.

   In order to improve performance HTTP/2 and HPACK uses naive text-
   compression, which incidentally decoupled the on-the-wire
   serialization from the data model.

   During the development of HPACK it became evident that significantly
   bigger gains were available if semantic compression could be used,
   most notably with timestamps.  However, the lack of a common data
   structure for HTTP headers would make semantic compression one long
   list of special cases.

   Parallel to this, various proposals for how to fulfill data-
   transportation needs, and to a lesser degree to impose some kind of
   order on HTTP headers, at least going forward were floated.

   All of these proposals, JSON, CBOR etc. run into the same basic
   problem: Their serialization is incompatible with [RFC7230]'s ABNF
   definition of 'field-value'.

   For binary formats, such as CBOR, a wholesale base64/85
   reserialization would be needed, with negative results for both
   debugability and bandwidth.

   For textual formats, such as JSON, the format must first be neutered
   to not violate field-value's ABNF, and then workarounds added to
   reintroduce the features just lost, for instance UNICODE strings, and
   suddenly it is no longer JSON anymore.

   This proposal starts from the other end, and builds and generalizes a
   data structure definition from existing HTTP headers, which means
   that HTTP/1 serialization and 'field-value' compatibility is built

   If all new HTTP headers are defined to fit into this Common Structure
   we have at least halted the proliferation of bespoke parsers and
   started to pave the road for semantic compression serializations of
   HTTP traffic.

Kamp                      Expires April 8, 2017                 [Page 2]
Internet-Draft                     I-D                      October 2016

1.1.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119

2.  Definition of HTTP header Common Structure

   The data model of Common Structure is an ordered sequence of named
   dictionaries.  Please see Appendix A for how this model was derived.

   The definition of the data model is on purpose abstract, uncoupled
   from any protocol serialization or programming environment
   representation, meant as the foundation on which all such
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